Recently, as energy issues and environmental issues are becoming increasingly serious, photovoltaic power generation with the use of solar cell elements that convert light energy directly into electrical energy is receiving attention.
Solar cell elements that are produced with semiconductor substrates such as a single-crystal silicon substrate and a poly-crystal silicon substrate are becoming mainstream. It is required to perform pn isolation for insulation between a p-type part and an n-type part in the solar cell element including a semiconductor substrate.
The methods using a laser are proposed as the method of performing pn isolation (see Patent Documents 1 to 4: Japanese Patent Application Laid-Open No. 05-75148 (1993), WO 2006/087786, U.S. Pat. No. 4,989,059 A, and Japanese Patent Application Laid-Open No. 2002-198546).